1. Field of the Invention
This invention relates to endoscopic surgical devices, and more particularly, to radio frequency energized endoscopic tissue dissection and coagulation devices.
2. Description of the Prior Art
U.S. Pat. No. 4,943,290 (Rexroth) discloses an electrolyte purging electrode tip suitable for use in an arthroscopic surgical system. In arthroscopic surgery, dissection or tissue cutting must take place within a joint cavity which is normally filled with an electrically conductive fluid including, for example, a local anaesthetic administered in a sodium chloride diluent or blood which also includes an electrically conductive sodium chloride diluent.
The presence of such electrically conductive fluids in the presence of the electrode tip causes unacceptably severe dissipation of electrical energy at the tip of the cutting electrode, requiring substantially increased levels of RF energy. In seeking to overcome unwanted RF power dissipation caused by operation of the RF-energized electrode cutting tip in an electrically conductive medium, higher RF power levels are required, but result in reduced cutting accuracy, significantly increased tissue heating and tissue smoking.
To solve this problem, Rexroth invented a system schematically illustrated in FIG. 1 (Prior Art) which injects a flow of non-conductive fluid (E.G. distilled water) out the end of a flexible tube to thereby surround the tip of the RF electrode with the electrically non-conductive fluid. By eliminating electrically conductive fluid from the substantially spherical region surrounding the exposed electrode tip, Rexroth avoids unwanted dissipation of RF energy and the heating power of the RF electrode is more easily concentrated on the tissue to be dissected or coagulated.
While the electrolyte purging electrode tip taught by Rexroth is quite acceptable for arthroscopic surgery, such techniques are unacceptable for other types of surgery. For example, the Rexroth electrolyte purging electrode tip system cannot be used for electrosurgery in the human brain which is surrounded by a fluid-filled medium in the form of cerebrospinal fluid (CSF). CSF represents a relatively highly conductive electrolyte which, if disturbed by the injection of a non-conductive electrolyte such as distilled or non-ionized water or the equivalent as taught by Rexroth, leads to unacceptable and potentially dangerous swelling of the brain tissue. The Rexroth system which requires the injection of a non-conductive fluid into the CSF electrolyte has therefore been unacceptable for neurosurgical applications.
For neurosurgical applications, tissue dissection is presently accomplished by mechanical biting or cutting devices or by laser heating devices which can also accomplish tissue coagulation. The biting and cutting devices as well as the laser device are packaged in relatively large diameter tubular bundles and require that a relatively large entrance aperture be bored into the human skull. Both the biting and cutting devices as well as the laser devices are also relatively inflexible and are therefore difficult to maneuver within the interior of the human brain. Because of the high level of sophistication of laser-energized tissue dissection and coagulation devices, laser systems typically cost on the order of about fifty thousand dollars.